Sole Structure for a Sports Shoe

ABSTRACT

A sole structure for a sports shoe that controls bendability of a forefoot region of the sole structure. The sole structure includes an upper midsole disposed on an upper side of the forefoot region of the sports shoe and formed of a soft elastic material, a lower midsole disposed under the upper midsole and formed of a soft elastic material, and an outsole that is disposed on a lower surface of the lower midsole and that has sole bent grooves extending substantially in a sole width direction. Both the lower surface of the upper midsole and the upper surface of the lower midsole have corrugated mating surfaces that are formed of wavy shapes extending substantially in a sole longitudinal direction. Ridge lines and trough lines of the wavy shapes of the upper midsole extend substantially in the sole width direction. The ridge lines of the wavy shapes of the upper midsole of a relatively higher hardness are overlapped with the sole bent grooves of the outsole in a vertical direction.

BACKGROUND OF THE INVENTION

The present invention relates generally to a sole structure for a sports shoe, and more particularly, to the sole structure that can control bendability of a forefoot region by preventing an excessive bending of the forefoot region.

EP3146862A2 discloses an article of footwear that includes a midsole having an undulating (i.e. zigzag) shape with alternating peaks and troughs in a sole longitudinal direction (see para. [0018] and FIGS. 1 and 2). The midsole has a gap formed between the adjacent peaks (i.e. above the trough between the adjacent peaks) and between the adjacent troughs (i.e. below the peak between the adjacent troughs). The gap between the adjacent peaks and the gap between the adjacent troughs extend across the entire width of the midsole (see para. [0018] and FIGS. 1 and 2).

In the sole structure described in EP3146862A2, when the troughs of the undulating (or zigzag-shaped) midsole contact the ground surface a compressive force is exerted on the troughs to distort the gaps above the troughs thus securing cushioning properties (see paras. [0019] to[0020]).

Japanese Patent No. 3403952 discloses a sole structure where a sole bent groove is formed in a forefoot region of an outsole and an upper midsole formed of a soft EVA sponge material is disposed on an upper surface of the outsole (see FIG. 1). The sole bent groove of the outsole penetrates the outsole in an outsole thickness direction and the upper midsole is exposed at a bottom portion of the sole bent groove.

In the sole structure described in JP Pat. No. 3403952, at the time of bending of the outsole, the forefoot region of the outsole bends along the sole bent groove thus securing sole bendability.

However, in the structure of EP3146862A2, at the time of bending of the midsole, an excessive bending is likely to occur locally at the troughs of the zigzag-shaped midsole. An occurrence of such a locally excessive bending causes an energy loss.

In the structure of JP Pat. No. 3403952, since the soft upper midsole is exposed at the bottom portion of the sole bent groove, an excessive bending is similarly likely to occur to cause an energy loss at the time of bending along the sole bent groove.

The present invention has been made in view of these circumstances and its object is to provide a sole structure for a sports shoe that can control bendability of a forefoot region by preventing an excessive bending of the forefoot region.

Other objects and advantages of the present invention will be obvious and appear hereinafter.

SUMMARY OF THE INVENTION

A sole structure for a sports shoe according to first aspect of the present invention includes an upper midsole that is disposed on an upper side of a forefoot region of the sports shoe and that is formed of a soft elastic material, a lower midsole that is disposed on a lower side of the forefoot region, that has an upper surface adapted to contact a lower surface of the upper midsole, and that is formed of a soft elastic material, and an outsole that is disposed on a lower surface of the lower midsole, that has a ground contact surface adapted to contact a ground surface, and that has a sole bent groove extending substantially in a sole width direction. Both the lower surface of the upper midsole and the upper surface of the lower midsole have a corrugated surface that is formed of wavy shapes extending substantially in a sole longitudinal direction, ridge lines and trough lines of the wavy shapes extend substantially in the sole width direction, and the upper midsole and the lower midsole have a hardness difference. At least a portion of the ridge lines of the wavy shapes of the upper midsole or the lower midsole that has a relatively higher hardness is overlapped with the sole bent groove of the outsole in a vertical direction.

According to the first aspect of the present invention, as above-mentioned, both the lower surface of the upper midsole and the upper surface of the lower midsole have a corrugated surface, the upper midsole and the lower midsole have a hardness difference, at least a portion of the ridge lines of the wavy shapes of the upper midsole or the lower midsole that has a relatively higher hardness is overlapped with the sole bent groove of the outsole in the vertical direction, and the ridge lines of the wavy shapes of the lower surface of the upper midsole or the upper surface of the lower midsole that has a relatively higher hardness are disposed at the position of the sole bent groove of the outsole. That is, at the position of the sole bent groove of the outsole, a thick part (i.e. a high-rigidity part) of the upper midsole of a greater hardness that has a corrugated surface on a lower surface thereof, or a thick part (i.e. a high-rigidity part) of the lower midsole of a greater hardness that has a corrugated surface on an upper surface thereof is disposed.

When the forefoot region of the sole structure is going to bend along the sole bent groove of the outsole at the time of bending of the sole structure, the thick part of the upper midsole or the lower midsole of a relatively greater hardness disposed at the sole bent groove is also going to bend at the same time. However, since such a thick part is a high-rigidity part, it has a greater bending resistance and it thus prevents an excessive bending locally along the sole bent groove of the sole structure. Thereby, bendability of the forefoot region can be controlled and an occurrence of an energy loss resulted from a locally excessive bending can be prevented.

A sole structure for a sports shoe according to second aspect of the present invention includes an upper midsole that is disposed on an upper side of a forefoot region of the sports shoe and that is formed of a soft elastic material, a lower midsole that is disposed on a lower side of the forefoot region, that has an upper surface adapted to contact a lower surface of the upper midsole, and that is formed of a soft elastic material, and an outsole that is disposed on a lower surface of the lower midsole, that has a ground contact surface adapted to contact a ground surface, and that has a sole bent groove extending substantially in a sole width direction. Either one of the lower surface of the upper midsole or the upper surface of the lower midsole has a corrugated surface that is formed of wavy shapes extending substantially in a sole longitudinal direction, ridge lines and trough lines of the wavy shapes extend substantially in the sole width direction. At least a portion of the ridge lines of the wavy shapes is overlapped with the sole bent groove of the outsole in a vertical direction.

According to second aspect of the present invention, as above-mentioned, at least a portion of the ridge lines of the wavy shapes provided either at the lower surface of the upper midsole or the upper surface of the lower midsole is overlapped with the sole bent groove of the outsole in the vertical direction, and the ridge lines of the wavy shapes of the lower surface of the upper midsole or the ridge lines of the wavy shapes of the upper surface of the lower midsole are disposed at the position of the sole bent groove of the outsole. That is, at the position of the sole bent groove of the outsole, a thick part (i.e. a high-rigidity part) of the upper midsole that has a corrugated surface on the lower surface thereof, or a thick part (i.e. a high-rigidity part) of the lower midsole that has a corrugated surface on the upper surface thereof is disposed.

When the forefoot region of the sole structure is going to bend along the sole bent groove of the outsole at the time of bending of the sole structure, the thick part of the upper midsole or the lower midsole disposed at the position on of the sole bent groove is also going to bend at the same time. However, since such a thick part is a high-rigidity part, it has a greater bending resistance and it thus prevents an excessive bending locally along the sole bent groove of the sole structure. Thereby, bendability of the forefoot region can be controlled and an occurrence of an energy loss resulted from the locally excessive bending can be prevented.

The ridge lines of the wavy shapes may be overlapped with the sole bent groove in the vertical direction either at a medial side part, a lateral side part, or a sole laterally central part of the forefoot region.

The bent groove may comprise a first sole bent groove and a second sole bent groove that are spaced apart on opposite sides of a metatarsophalangeal joint of a foot of a shoe wearer in the sole longitudinal direction.

A third sole bent groove may be provided between the first sole bent groove and the second sole bent groove and the third sole bent groove may be spaced apart from the first sole bent groove and the second sole bent groove in the sole longitudinal direction.

The sole bent groove may open at least at either one of a medial side end portion or a lateral side end portion of the forefoot region.

The sole bent groove may close at both a medial side end portion and a lateral side end portion of the forefoot region.

The sole bent groove may include a slit extending through a thickness of the outsole.

The sole bent groove may further include a recessed groove formed at a position corresponding to the slit on the lower surface of the lower midsole.

The ridge lines and trough lines of the wavy shapes may extend across an entire width of the forefoot region.

The ridge lines and trough lines of the wavy shapes may be disposed only at a sole laterally central side portion of the forefoot region.

The upper surface of the lower midsole or the lower surface of the upper midsole without the corrugated surfaces may have a planar surface, and there may be formed a gap between the planar surface and the lower surface of the upper midsole or the upper surface of the lower midsole. Thus, when a load is transferred to the forefoot region of the sole structure, cushioning properties is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention.

FIG. 1 is a bottom schematic view of a sole structure for a sports shoe according to an embodiment of the present invention.

FIG. 2 is a medial side view of the sole structure of FIG. 1.

FIG. 3 is a lateral side view of the sole structure of FIG. 1.

FIG. 4 is a longitudinal sectional view of FIG. 1 taken along line IV-IV.

FIG. 5 is a cross sectional view of FIG. 1 taken along line V-V of FIG. 1.

FIG. 6 is a cross sectional view of FIG. 1 taken along line VI-VI of FIG. 1.

FIG. 7 is a cross sectional view of FIG. 1 taken along line VII-VII of FIG. 1.

FIG. 8 is a cross sectional view of FIG. 1 taken along line VIII-VIII of FIG. 1.

FIG. 9 is a bottom schematic view illustrating the sole structure of FIG. 1 together with an anatomical or bone structure of a foot to explain the positional relation between a sole bent groove and the foot anatomical structure.

FIG. 10 is a partially enlarged view of FIG. 2.

FIG. 11 is a partially enlarged view of FIG. 3.

FIG. 12 is a partially enlarged view of FIG. 4.

FIG. 13 is a partially enlarged view of FIG. 10 to explain a depth of the sole bent groove.

FIG. 14 is a bottom schematic view of a sole structure for a sports shoe according to a first alternative embodiment of the present invention.

FIG. 15 is a medial side view of the sole structure of FIG. 14.

FIG. 16 is a lateral side view of the sole structure of FIG. 14.

FIG. 17 is a longitudinal sectional view of FIG. 14 taken along line XVII-XVII.

FIG. 18 is a partially enlarged view of FIG. 15.

FIG. 19 is a partially enlarged view of FIG. 16.

FIG. 20 is a partially enlarged view of FIG. 17.

FIG. 21 is a partially enlarged view of FIG. 19 to explain a depth of the sole bent groove.

FIG. 22 is a bottom schematic view of a sole structure for a sports shoe according to a second alternative embodiment of the present invention.

FIG. 23 is a medial side view of the sole structure of FIG. 22.

FIG. 24 is a lateral side view of the sole structure of FIG. 22.

FIG. 25 is a longitudinal sectional view of FIG. 22 taken along line XXV-XXV.

FIG. 26 is a medial side view of a sole structure for a sports shoe according to a third alternative embodiment of the present invention.

FIG. 27 is a medial side view of a portion of a sole structure for a sports shoe according to a fourth alternative embodiment of the present invention.

FIG. 28 is a medial side view of a portion of a sole structure for a sports shoe according to a fifth alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIGS. 1 to 13 show a sole structure for a sports shoe according to an embodiment of the present invention. Here, a running shoe is taken for an example as a sports shoe. In the following explanation, “forward (front side/front)” and“rearward (rear side/rear)” designate a forward direction and a rearward direction of the shoe, respectively, “upward (upper side/upper)” and “downward (lower side/lower)” designate an upward direction and a downward direction of the shoe, respectively, and “a width or lateral direction” designates a crosswise direction of the shoe. For example, in the case of FIG. 1, “forward” and “rearward” designate “upward” and “downward” in FIG. 1 respectively, “upward” and “downward” designate “into the page” and “out of the page” of FIG. 1 respectively, and“a width direction” designates “left to right direction” in FIG. 1. Also, in FIG. 1, H, M and F designate a heel region, midfoot region and forefoot region of the sole structure, respectively.

As shown in FIGS. 1 to 4, a sole structure 1 includes an upper midsole 2 disposed on an upper side of the sole structure 1, a lower midsole 3 disposed on a lower side of the sole structure 1, and an outsole 4 attached on a lower or bottom surface of the lower midsole 3. The upper and lower midsoles 2, 3 extend from the heel region H through the midfoot region M to the forefoot region F of the sole structure 1. For illustration purposes, grooves formed on a bottom surface of the outsole 4 for improving anti-slip capacity, gripping properties, durability and design and for weight reduction are not shown.

An upper or top surface 2 a of the upper midsole 2 constitutes a foot-sole contact surface that directly contacts a foot sole of a shoe wearer or that indirectly contacts the foot sole of the wearer via an insole and the like disposed on the upper surface 2 a. As shown in FIGS. 2 to 4, the upper surface 2 a extends from the heel region H through the midfoot region M to the forefoot region F of the sole structure 1. On opposite sides of the upper surface 2 a in the sole width direction, a pair of upraised portions 20 that extends upwardly are provided, as shown in FIGS. 5 to 8.

As shown in FIGS. 1 to 4, a lower surface 2 b of the upper midsole 2 has a corrugated surface and an upper surface 3 a of the lower midsole 3 also has a corrugated surface that corresponds to the corrugated lower surface 2 b of the upper midsole 2. The lower surface 2 b of the upper midsole 2 and the upper surface 3 a of the lower midsole 3 are fixedly attached to each other by bonding and the like with crests and troughs of each of the corrugated surfaces engaged with each other. FIGS. 2 to 4 show that each of wavy shapes of the upper and lower midsoles 2, 3 extends from the heel region H through the midfoot region M to the forefoot region F of the sole structure 1. However, in the sole structure 1 of this embodiment, each of wavy shapes of the upper and lower midsoles 2, 3 has only to be provided at least at the forefoot region F of the sole structure 1.

Ridge (or crest) lines and trough (or ravine) lines of the wavy shapes on the lower surface 2 b of the upper midsole 2 are shown in dotted lines in the forefoot region F of FIG. 1. Here, the ridge lines of the wavy shapes are lines that connect vertexes of the convexly curved portions of the wavy shapes and the trough lines of the wavy shapes are lines that connect the deepest parts of the concavely curved portions of the wavy shapes. The ridge lines of the wavy shapes of the lower surface 2 b of the upper midsole 2 correspond to the trough lines of the wavy shapes of the upper surface 3 a of the lower midsole 3. Similarly, the trough lines of the wavy shapes of the lower surface 2 b of the upper midsole 2 correspond to the ridge lines of the wavy shapes of the upper surface 3 a of the lower midsole 3. In FIG. 1, five dotted lines are shown, but in these dotted lines, the dotted lines 2 b 1 designate the ridge lines of the wavy shapes of the lower surface 2 b of the upper midsole 2 and the dotted lines 2 b ₂ located between longitudinally adjacent dotted lines 2 b 1 designate the trough lines of the wavy shapes of the lower surface 2 b of the upper midsole 2.

These ridge lines 2 b ₁ and the trough lines 2 b ₂ extend substantially in the sole width direction and both are gently curved lines that extends along the entire width of the sole. Here, the term, “substantially” means the following two cases:

i) The ridge lines 2 b ₁ and the trough lines 2 b ₂ are width lines that are exactly perpendicular to a longitudinal centerline of the sole (see line IV-IV of FIG. 1); and

ii) The ridge lines 2 b ₁ and the trough lines 2 b ₂ are lines that angle to the width lines to extend obliquely across the longitudinal centerline.

Also, each of the ridge lines 2 b ₁ and the trough lines 2 b ₂ angles gradually to a medial side toward the forward direction so as to follow the direction of a load transfer during running and the wavy shapes of the lower surface 2 b of the upper midsole 2 progresses substantially in the sole longitudinal direction. Similarly, the term, “substantially” means the following two cases:

i) The wavy shapes progress exactly along the longitudinal centerline of the sole (see line IV-IV of FIG. 1); and

ii) The wavy shapes progress obliquely relative to the longitudinal centerline.

As shown in FIG. 1, the sole structure 1 has a plurality of sole bent grooves G₁, G₂, G₃, G₃′ on a bottom side of the forefoot region F. Each of the sole bent grooves G₁, G₂, G₃, G₃′ is located at a position to vertically overlap with each of the ridge lines 2 b ₁ of the wavy shapes of the lower surface 2 b of the upper midsole 2. In FIGS. 2 to 4, the ridge lines 2 b ₁ extend in a direction perpendicular to each of the drawings and are disposed above and face the corresponding sole bent grooves G₁, G₂, G₃, G₃′. In this embodiment, the ridge lines 2 b ₁ vertically overlap with the sole bent grooves G₁, G₂, G₃, G₃′ across the entire width of the sole, i.e. from the medial side part through the laterally central part to the lateral side part of the forefoot region F. As viewed from below, the ridge lines 2 b ₁ extend along the sole bent grooves G₁, G₂, G₃, G₃′ inside the sole bent grooves G₁, G₂, G₃, G₃′. Therefore, the sole bent grooves G₁, G₂, G₃, G₃′ also extend substantially in the sole width direction.

As shown in FIG. 9, the sole bent grooves G₁, G₂ are disposed in front of and to the rear of the metatarsophalangeal joint MP of the foot of the shoe wearer, respectively. That is, the sole bent grooves G₁, G₂ are spaced away from each other on opposite sides of the metatarsophalangeal joint MP. The first sole bent groove G₁ extends from the proximal end of the first distal phalanx DP₁ (or the distal end of the first proximal phalanx PP₁) on the medial side through the distal end of the second middle phalanx MP₂ toward the lateral side. The second sole bent groove G₂ extends from the central part of the first metatarsus MB₁ to the rear of the thenar eminence TE on the medial side toward the distal end of the fifth metatarsus MB₅ on the lateral side. The third sole bent grooves G₃, G₃′ are disposed between and spaced away from the first sole bent groove G₁ and the second sole bent groove G₂. The third sole bent groove G₃ is a short groove or a cutout disposed at and near the metatarsophalangeal joint MP on the medial side. The third sole bent groove G₃′ extends from the lateral side through the fifth distal phalanx DP₅ toward the laterally central part.

The first and second sole bent grooves G₁, G₂ open at both the medial side end and the lateral side end of the forefoot region F (see FIGS. 2 and 3). The third sole bent groove G₃ opens only at the medial side end of the forefoot region F and the third sole bent groove G₃′ opens only at the lateral side end of the forefoot region F (see FIG. 1). By these sole bent grooves G₁, G₂, G₃, G₃′, the outsole 4 is divided into two outsole parts 4A and 4B at the forefoot region F (see FIG. 1). In an area from the midfoot region M to the heel region H, the outsole 4 is divided into outsole parts 4C₁, 4D on the medial side and outsole parts 4C₂, 4C₃, 4C₄, 4D on the lateral side (see FIG. 1). At the central portion of the heel region H of the sole structure 1, a recess 35 is formed and the outsole part 4C₁ and the outsole parts 4C₃, 4C₄ are spaced away from each other in the sole width direction via the recess 35. As shown in FIGS. 7 and 8, the recess 35 is formed of a concave groove on the lower midsole 3.

As shown in FIGS. 10 to 12, the first sole bent groove G₁ comprises a slit 40 that pierces the outsole 4 in the thickness direction to divide the outsole 4 into the outsole parts 4A and 4B and a concave groove 30 that is formed on the lower surface 3 b of the lower midsole 3, that is located at a position corresponding to the slit 40, and that is in connection with the slit 40. The second sole bent groove G₂ comprises a slit 41 that pierces the outsole 4 in the thickness direction to divide the outsole 4 into the outsole parts 4B and 4C₁, 4C₂ and a concave groove 31 that is formed on the lower surface 3 b of the lower midsole 3, that is located at a position corresponding to the slit 41, and that is in connection with the slit 41. The third sole bent groove G₃ comprises a slit 42 that pierces the outsole 4 in the thickness direction and a concave groove 32 that is formed on the lower surface 3 b of the lower midsole 3, that is located at a position corresponding to the slit 42, and that is in connection with the slit 42. The third sole bent groove G₃′ comprises a slit 42′ that pierces the outsole 4 in the thickness direction and a concave groove 32′ that is formed on the lower surface 3 b of the lower midsole 3, that is located at a position corresponding to the slit 42′, and that is in connection with the slit 42′. In FIGS. 10 to 12, each of the positions of the ridge lines 2 b ₁ of the wavy shape formed on the lower surface 2 b of the lower midsole 2 are shown by a black dot.

Here, the opening width and the depth of each of the sole bent grooves G₁, G₂, G₃, G₃′ are defined as follows using FIG. 13. In FIG. 13, an example of the third sole bent groove G₃ is shown, but the same applies to other sole bent grooves.

As shown in FIG. 13, the opening width of the third sole bent groove G₃ is defined as the opening width W of the slit 42 of the outsole 4, and the depth of the third sole bent groove G₃ is defined as the depth d of the concave groove 32, which is measured from the lower surface 3 b (i.e. the outsole-bonding surface) of the lower midsole 3. Specifically, the opening width W and the depth d is set at

W=3-18 mm (preferably 7 mm)

d=0.5-10 mm (preferably 2 mm)

In this example, the opening width w of the concave groove 32 formed on the lower surface 3 b of the lower midsole 3 is smaller than the opening width W of the slit 42 of the outsole 4. At an opening edge portion of the concave groove 32, there is formed a rim 32 r that protrudes downwardly (or to the right in FIG. 13). The rim 32 r is provided for reinforcement of the concave groove 32, prevention of slip/peeling-off of the outsole portion 4B, identification of the bonding position and the like.

The upper and lower midsoles 2, 3 are formed of soft elastic materials, more specifically, thermoplastic resin such as ethylene-vinyl acetate copolymer (EVA) and the like, foamed thermoplastic resin, thermosetting resin such as polyurethane (PU) and the like, foamed thermosetting resin, elastomers of these resin, rubber materials such as butadiene rubber, chloroprene rubber and the like, or foamed rubber materials.

A hardness of the upper midsole 2 is greater than a hardness of the lower midsole 3. Specifically, the hardness of the upper midsole 2 is set to, for example 60±4 C in the Asker C scale and the hardness of the lower midsole 3 is set to, for example 50±4 C in the Asker C scale. A difference between the hardness of the upper midsole 2 and the hardness of the lower midsole 3 is preferably approximately 5 C.

The outsole 4 is formed of a hard elastic member. specifically, the outsole 4 is formed of thermoplastic resin such as thermo plastic polyurethane (TPU), polyamide elastomer (PAE) and the like, thermosetting resin such as epoxy and the like, or solid rubber and the like. A hardness of the outsole 4 is set to, for example 60A in the Asker A scale.

According to this embodiment, when the forefoot region F of the sole structure 1 bends during running, the forefoot region F bends along the sole bent groove G₂ on the rear side of the forefoot region F, the sole bent groove G₃, G₃′ at the longitudinally intermediate position of the forefoot region F, and the sole bent groove G₂ on the front side of the forefoot region F, in order.

At this time, both the lower surface 2 b of the upper midsole 2 and the upper surface 3 a of the lower midsole 3 have corrugated surfaces, the ridge lines 2 b ₁ of the wavy shapes of the upper midsole 2 of a relatively higher hardness are overlapped with the sole bent grooves G₁, G₂, G₃, G₃′ of the outsole 4 in a vertical direction, and at the positions of the sole bent grooves G₁, G₂, G₃, G₃′ of the outsole 4, the ridge lines 2 b ₁ of the wavy shapes of the upper midsole 2 of a relatively higher hardness are located (see FIG. 1). That is, the ridge lines 2 b ₁ are disposed above and face the corresponding sole bent grooves G₁, G₂, G₃, G₃′ (see FIGS. 2 to 4 and 10 to 13). Therefore, a thick part (i.e. a high-rigidity part) of the upper midsole 2 having a higher hardness and a corrugated surface on the lower surface 2 b thereof is disposed at each of the positions of the sole bent grooves G₁, G₂, G₃, G₃′ of the outsole 4.

Therefore, when the forefoot region F is going to bend along the sole bent grooves G₁, G₂, G₃, G₃′ of the outsole 4 during bending of the sole structure 1, the thick parts of the relatively harder upper midsole 2 disposed at the positions of the sole bent grooves G₁, G₂, G₃, G₃′ are going to bend at the same time. At this moment, since these thick parts are high-rigidity parts, an excessive bending locally along the sole bent grooves G₁, G₂, G₃, G₃′ of the sole structure 1 can be restricted. Thereby, the sole structure 1 can equally bend in the sole longitudinally direction, and bendability of the forefoot region F can thus be controlled. As a result, an occurrence of an energy loss resulted from locally excessive bending can be prevented.

First Alternative Embodiment

In the above-mentioned embodiment, an example was shown in which the sole bent grooves G₁, G₂, G₃, G₃′ provided at the forefoot region F of the sole structure 1 comprise the slits (or through grooves) 40, 41, 42, 42′ passing through the outsole 4 and the concave grooves (or blind grooves) 30, 31, 32, 32′ formed on the lower midsole 3, respectively but application of the present invention is not limited to such an example.

FIGS. 14 to 21 show a sole structure of a sports shoe according to a first alternative embodiment. In these drawings, like reference numbers indicate identical or functionally similar elements. Here, an indoor sports shoe is taken for an example of the sports shoe. As shown in FIGS. 14 to 21, in this first alternative embodiment, there are provided sole bent grooves G₁, G₂, G₃ at the forefoot region F of the sole structure 1, which are formed of concave grooves (or blind grooves) 45, 46, 47 respectively formed on the ground contact surface of the outsole 4. That is, the sole bent grooves G₁, G₂, G₃ do not pass through the outsole 4.

Also, similar to the above-mentioned embodiment, the ridge lines 2 b ₁ of the wavy surfaces of the lower surface 2 b of the upper midsole 2 are vertically overlapped with the sole bent grooves G₁, G₂, G₃ of the outsole 4, that is, each of the ridge lines 2 b ₁ is disposed upwardly opposite the corresponding sole bent grooves G₁, G₂, G₃, and the upper midsole 2 is harder than the lower midsole 3.

The opening width and the depth of each of the sole bent grooves G₁, G₂, G₃ are defined as follows using FIG. 21. In FIG. 21, an example of the third sole bent groove G₃ is shown, but the same applies to other sole bent grooves.

As shown in FIG. 21, the opening width of the third sole bent groove G₃ is defined as a distance W between the oppositely disposed opening edge portions of the third sole bent groove G₃, and the depth of the third sole bent groove G₃ is defined as a thickness d of a thin part at the bottom portion of the third sole bent groove G₃. Specifically, the opening width W and the depth d is set at

W=1-15 mm (preferably 4 mm)

d=1-2 mm (preferably 1 mm)

When the forefoot region F of the sole structure 1 bends during exercise, the forefoot region F bends along the sole bent grooves G₁, G₂, G₃. At this time, as above-mentioned, both the lower surface 2 b of the upper midsole 2 and the upper surface 3 a of the lower midsole 3 have corrugated surfaces, the ridge lines 2 b ₁ of the wavy shapes of the upper midsole 2 of a relatively higher hardness are overlapped with the sole bent grooves G₁, G₂, G₃ of the outsole 4 in a vertical direction, and at the positions of the sole bent grooves G₁, G₂, G₃ of the outsole 4, the ridge lines 2 b ₁ of the wavy shapes of the upper midsole 2 of a relatively higher hardness are located (see FIG. 14). That is, the ridge lines 2 b ₁ are disposed above and opposite the corresponding sole bent grooves G₁, G₂, G₃ (see FIGS. 15 to 21). Therefore, a thick part (i.e. a high-rigidity part) of the upper midsole 2 having a higher hardness and a corrugated surface on the lower surface 2 b thereof is disposed at each of the positions of the sole bent grooves G₁, G₂, G₃ of the outsole 4.

Therefore, when the forefoot region F is going to bend along the sole bent grooves G₁, G₂, G₃ of the outsole 4 during bending of the sole structure 1, the thick parts of the relatively harder upper midsole 2 disposed at the positions of the sole bent grooves G₁, G₂, G₃ are going to bend at the same time. At this moment, since these thick parts are high-rigidity parts and thus have a greater bending resistance, an excessive bending locally along the sole bent grooves G₁, G₂, G₃ of the sole structure 1 can be restricted. Thereby, the sole structure 1 can equally bend in the longitudinally direction, and bendability of the forefoot region F can thus be controlled. As a result, an occurrence of an energy loss resulted from locally excessive bending can be prevented.

Second Alternative Embodiment

In the above-mentioned embodiment and the first alternative embodiment, an example was shown in which the ridge lines 2 b ₁ of the wavy shapes of the lower surface 2 b of the upper midsole 2 extend across the entire width of the sole (that is, from the medial side end to the lateral side end), but application of the present invention is not limited to such an example.

FIGS. 22 to 25 show a sole structure of a sports shoe according to a second alternative embodiment. Here, a running shoe is taken for an example of the sports shoe. In these drawings, like reference numbers indicate identical or functionally similar elements.

As shown in FIGS. 22 to 25, in this second alternative embodiment, at the longitudinally and laterally central part of the upper midsole 2 in the forefoot region F of the sole structure 1, there is formed a concavity 28 that opens to the side of the lower surface 2 b. In this example, the concavity 28 is a generally rectangular shaped blind hole that is formed on and opens to the lower surface 2 b. On the bottom surface of the concavity 28, a corrugated surface is formed, and ridge lines and trough lines of the wavy shapes are shown by dotted lines in FIG. 22. There are plural dotted lines drawn in FIG. 22. In these dotted lines, the dotted lines 2 b ₁ indicate the ridge lines of the wavy shapes of the bottom surface of the concavity 28, and the dotted lines 2 b ₂ located between the longitudinally adjacent dotted lines 2 b ₁ indicate the trough lines of the wavy shapes of the bottom surface of the concavity 28. As shown in FIG. 22, the ridge lines 2 b ₁ and the trough lines 2 b ₂ of the wavy shapes of the bottom surface of the concavity 28 in the upper midsole 2 are provided only at the sole lateral central portion of the forefoot region F and do not extend to the medial side end and to the lateral side end of the forefoot region F. Therefore, the corrugated surface of the concavity 28 of the upper midsole 2 does not appear at the medial and lateral side ends of the forefoot region F (see FIGS. 23 and 24).

Each of the ridge lines 2 b ₁ and the trough lines 2 b ₂ extends gently curvedly and substantially in the sole width direction. Here, the term, “substantially” means the following two cases similar to the above-mentioned embodiment:

i) The ridge lines 2 b ₁ and the trough lines 2 b ₂ are width lines that are exactly perpendicular to a longitudinal centerline of the sole; and

ii) The ridge lines 2 b ₁ and the trough lines 2 b ₂ are lines that angle to the width lines to extend obliquely across the longitudinal centerline.

Also, each of the ridge lines 2 b ₁ and the trough lines 2 b ₂ angles gradually to a medial side toward the forward direction so as to follow the direction of a load transfer during running and the wavy shapes of the bottom surface of the concavity 28 progress substantially in the sole longitudinal direction. Here, the term, “substantially” means the following two cases:

i) The wavy shapes progress exactly along the longitudinal centerline of the sole; and

ii) The wavy shapes progress obliquely relative to the longitudinal centerline.

Inside the concavity 28 of the upper midsole 2, a midsole insert 38 is housed. The midsole insert 38 is generally rectangular shaped and sized to correspond to the concavity 28. A top surface 38 a of the midsole insert 38 has no wavy shapes, and it is a planar or gently curved surface and contacts the corrugated bottom surface of the concavity 28 of the upper midsole 2. That is, the top surface 38 a of the midsole insert 38 contacts the ridge lines 2 b ₁ of the corrugated surface of the concavity 28 of the upper midsole 2. There are formed a gap S between the upper surface 38 a of the midsole insert 38 and the trough lines 2 b ₂ of the corrugated surface of the concavity 28 of the upper midsole 2.

As shown in FIG. 22, the sole structure 1 includes a plurality of sole bent grooves G₁, G₂, G₃, G₃′ on the side of the lower surface in the forefoot region F. The midsole insert 38 is disposed between the sole bent grooves G₁ and G₂. The sole bent groove G₃′ is disposed at the position where the sole bent groove G₃′ is vertically overlapped with any of the ridge lines 2 b ₁ of the wavy shapes of the concavity 28 of the upper midsole 2. That is, any of the ridge lines 2 b ₁ of the wavy shapes of the concavity 28 of the upper midsole 2 is disposed above and opposite the sole bent groove G₃′. In this example, a portion of the ridge lines 2 b ₁ is vertically overlapped with the bent groove G₃′ at the sole laterally central part of the forefoot region F and disposed inside and extends along the sole bent groove G₃′ as viewed from above or below.

As shown in FIGS. 23 to 25, the upper midsole 2 extends from the heel region H through the midfoot region H to the forefoot region F of the sole structure 1. The lower midsole 3 is provided mainly at the heel region H of the sole structure 1. Between the upper and lower midsoles 2, 3 in the heel region H, a corrugated sheet 5 is provided. The corrugated sheet 5 has wavy shapes that progress in the sole longitudinal direction and is formed of a hard elastic member. On each of the mating surfaces of the upper and lower midsoles 2, 3 that sandwich the corrugated sheet 5, wavy shapes are formed that correspond to the wavy shapes of the corrugated sheet 5 and cushioning holes are optionally formed.

The outsole 4 is divided into two outsole parts 4A and 4B in the forefoot region F by the sole bent grooves G₁, G₂, G₃, G₃′ provided on the bottom side of the forefoot region F of the sole structure 1. In an area extending from the midfoot region M to the heel region H, the outsole 4 is divided into two outsole parts 4C₁, 4C₁′, 4D on the medial side and four outsole parts 4C₂, 4C₃, 4C₄, 4D on the lateral side (see FIG. 22).

As shown in FIGS. 22 to 24, the first sole bent groove G₁ comprises a slit 40 that divides the outsole 4 into the outsole parts 4A and 4B (that is, the slit 40 passes through the outsole 4 in the thickness direction), and a concave groove 25 formed on the lower surface 2 b of the upper midsole 2 and located at a position corresponding to the slit 40. The second sole bent groove G₂ comprises a slit 41 that divides the outsole 4 into the outsole parts 4B and 4C₁′, 4C₂ (that is, the slit 41 passes through the outsole 4 in the thickness direction), and a concave groove 26 formed on the lower surface 2 b of the upper midsole 2 and located at a position corresponding to the slit 41. The third sole bent groove G₃ comprises a slit 42 that passes through the outsole 4 in the thickness direction and a concave groove 27 formed on the lower surface 2 b of the upper midsole 2 and located at a position corresponding to the slit 42. The third sole bent groove G₃′ comprises a slit 42′ that passes through the outsole 4 in the thickness direction and a concave groove 27′ formed on the lower surface 2 b of the upper midsole 2 and located at a position corresponding to the slit 42′.

The opening width and the depth of each of the sole bent grooves G₁, G₂, G₃, G₃′ are defined in the same manner as the above-mentioned embodiment. That is, as the opening width of each of the sole bent grooves, the opening width of each of the slits of the outsole 4 is employed, and as the depth of each of the sole bent grooves, the depth measured from the lower surface 2 b of the upper midsole 2 (i.e. the outsole-bonding surface of the upper midsole 2) is employed. Specific values are similar to those shown in the above-mentioned embodiment.

The upper midsole 2 and the midsole insert 38 are formed of a soft elastic material as with the above-mentioned embodiment, but unlike the above-mentioned embodiment, a hardness of the upper midsole 2 is not necessarily greater than a hardness of the midsole insert 38. A hardness difference between the upper midsole 2 and the midsole insert 38 may be null.

The reason is as follows:

Since the corrugated bottom surface of the concavity 28 of the upper midsole 2 contacts the planar upper surface 38 a of the midsole insert 38, only the ridge lines 2 b ₁ of the corrugated bottom surface is in contact with the upper surface 38 a and a gap S is formed between the trough lines 2 b ₂ and the upper surface 38 a. Therefore, even if the upper midsole 2 and the midsole insert 38 have the same hardness, a portion including the ridge lines 2 b ₁ of the upper midsole 2 is thick and thus its rigidity becomes greater than other portions of the upper midsole 2.

When the forefoot region F of the sole structure 1 bends during running, the forefoot region F is going to bend along the sole bent groove G₂ at the rear of the forefoot region F, the sole bent grooves G₃, G₃′ at the longitudinally intermediate position of the forefoot region F, and the sole bent groove G₁ in front of the forefoot region F, in order.

At this time, the bottom surface of the concavity 28 of the upper midsole 2 has a corrugated surface and portions including the ridge lines 2 b ₁ (i.e. thick parts of higher rigidity) are vertically overlapped with and disposed opposite the sole bent grooves G₃′ (see FIGS. 22 and 25).

Therefore, when the forefoot region F is going to bend along the sole bent grooves G₃′ of the outsole 4 during bending of the sole structure 1, the portions including the ridge lines 2 b of the upper midsole 2 disposed at the position of the sole bent groove G₃′ are going to bend at the same time. At this moment, since these portions are high-rigidity parts and thus have a greater bending resistance, an excessive bending locally along the sole bent grooves G₃′ of the sole structure 1 can be restricted. Thereby, the sole structure 1 can equally bend in the longitudinally direction, and bendability of the forefoot region F can thus be controlled. As a result, an occurrence of an energy loss resulted from locally excessive bending can be prevented. In addition, the midsole insert 38 may extend to either one of the medial side end or the lateral side end of the forefoot region F.

Third Alternative Embodiment

FIG. 26 shows a third alternative embodiment of the present invention and it corresponds to FIG. 2 of the above-mentioned embodiment. In FIG. 26, like reference numbers indicates identical or functionally similar elements to those in FIG. 2. In the above-mentioned embodiment, an example was shown in which the hardness of the upper midsole 2 is higher than the hardness of the lower midsole 3, but in this third alternative embodiment, contrary to such an example, the hardness of the lower midsole 3 is higher than the hardness of the upper midsole 2.

Specifically, the hardness of the lower midsole 3 is set to, for example 60±4 C in the Asker C scale and the hardness of the upper midsole 2 is set to, for example 50±4 C in the Asker C scale. A difference between the hardness of the upper midsole 2 and the hardness of the lower midsole 3 is preferably approximately 5 C.

Also, in this third alternative embodiment, a phase of the wavy shapes of the upper and lower midsoles 2, 3 relative to each of the sole bent grooves G₁, G₂, G₃ differs from that in the above-mentioned embodiment. In the above-mentioned embodiment, the ridge lines 2 b ₁ of the wavy shapes of the upper midsole 2 are disposed opposite the sole bent grooves G₁, G₂, G₃, but in this third alternative embodiment, the ridge lines 3 a ₁ of the wavy shapes of the lower midsole 3 are disposed opposite the sole bent grooves G₁, G₂, G₃.

In this way, at the positions of the sole bent grooves G₁, G₂, G₃, the ridge lines 3 a ₁ of the wavy shapes of the upper surface of the lower midsole 3 having a relatively greater hardness are disposed, that is, thick parts (or high-rigidity parts) of the lower midsole 3 of a greater hardness are disposed. When the forefoot region F of the sole structure 1 is going to bend along the sole bent grooves G₁, G₂, G₃ during exercise such as running, the thick parts (or high-rigidity parts) of the lower midsole 3 of a relatively greater hardness disposed at the positions of the sole bent grooves G₁, G₂, G₃ are going to bend at the same time, which generates a greater bending resistance. Thereby, a locally excessive bending along the sole bent grooves G₁, G₂, G₃ of the sole structure 1 can be restricted. In such a manner, the sole structure 1 is able to bend equally in the longitudinally direction to control bendability of the forefoot region F. As a result, an occurrence of an energy loss resulted from locally excessive bending can be prevented.

Fourth Alternative Embodiment

FIG. 27 shows a fourth alternative embodiment of the present invention and it corresponds to FIG. 18 of the first alternative embodiment. In FIG. 27, like reference numbers indicates identical or functionally similar elements to those in FIG. 18. In the above-mentioned embodiment, an example was shown in which both the upper midsole 2 and the lower midsole 3 have corrugated surfaces formed thereon, but in this fourth alternative embodiment, contrary to such an example, only the lower surface 2 b of the upper midsole 2 has a corrugated surface formed thereon, the upper surface 3 a of the lower midsole 3 has no corrugated surface formed thereon and has a planar surface or a gently curved surface formed thereon.

The ridge lines 2 b ₁ of the corrugated lower surface 2 b of the upper midsole 2 contact the planar upper surface 3 a of the lower midsole 3, the trough lines 2 b ₂ do not contact the planar upper surface 3 a of the lower midsole 3, and there is formed a gap S between the trough lines 2 b ₂ and the planar upper surface 3 a of the lower midsole 3. Also, the ridge lines 2 b ₁ of the upper midsole 2 and thus thick parts or high-rigidity parts of the upper midsole 2 are vertically overlapped with or disposed opposite the positions of the sole bent grooves G₁, G₂ of the outsole 4.

In such a manner, since the thick parts or high-rigidity parts of the upper midsole 2 are disposed at the positions of the sole bent grooves G₁, G₂, when the forefoot region F of the sole structure 1 is going to bend along the sole bent grooves G₁, G₂ during exercise such as running, the thick parts or high-rigidity parts of the upper midsole 2 disposed at the positions of the sole bent grooves G₁, G₂ are going to bend at the same time, which generates a greater bending resistance, thus restricting an excessive bending locally along the sole bent grooves G₁, G₂ of the sole structure 1. Thereby, the sole structure 1 can bend equally in the longitudinally direction to control bendability of the forefoot region F. As a result, an occurrence of an energy loss resulted from locally excessive bending can be prevented.

Additionally, in this fourth alternative embodiment, as with the second alternative embodiment, the hardness of the upper midsole 2 is not necessarily higher than the hardness of the lower midsole 3 and a hardness difference does not necessarily exist between the upper and lower midsoles 2, 3. That is because a rigidity of an area including the ridge lines 2 b ₁ of the upper midsole 2 is higher than rigidities of other areas even if the upper and lower midsoles 2, 3 have the same hardness.

Fifth Alternative Embodiment

FIG. 28 shows a fifth alternative embodiment of the present invention and it corresponds to FIG. 18 of the first alternative embodiment. In FIG. 28, like reference numbers indicates identical or functionally similar elements to those in FIG. 18. In the above-mentioned embodiment, an example was shown in which both the upper midsole 2 and the lower midsole 3 have corrugated surfaces formed thereon, but in this fifth alternative embodiment, contrary to such an example, only the upper surface 3 a of the lower midsole 3 has a corrugated surface formed thereon, the lower surface 2 b of the upper midsole 2 has no corrugated surface formed thereon and has a planar surface or a gently curved surface formed thereon.

The ridge lines 3 a ₁ of the corrugated upper surface 3 a of the lower midsole 3 contact the planar lower surface 2 b of the upper midsole 2, the trough lines 3 a ₂ do not contact the lower planar lower surface 2 b of the upper midsole 2, and there is formed a gap S between the trough lines 3 a ₂ and the planar lower surface 2 b of the upper midsole 2. Also, the ridge lines 3 a ₁ of the lower midsole 3 and thus thick parts or high-rigidity parts of the lower midsole 3 are vertically overlapped with or disposed opposite the positions of the sole bent grooves G₁, G₂ of the outsole 4.

In such a manner, since the thick parts or high-rigidity parts of the lower midsole 3 are disposed at the positions of the sole bent grooves G₁, G₂, when the forefoot region F of the sole structure 1 is going to bend along the sole bent grooves G₁, G₂ during exercise such as running, the thick parts or high-rigidity parts of the lower midsole 3 disposed at the positions of the sole bent grooves G₁, G₂ are going to bend at the same time, which generates a greater bending resistance, thus restricting an excessive bending locally along the sole bent grooves G₁, G₂ of the sole structure 1. Thereby, the sole structure 1 can bend equally in the longitudinally direction to control bendability of the forefoot region F. As a result, an occurrence of an energy loss resulted from locally excessive bending can be prevented.

Additionally, in this fifth alternative embodiment, the hardness of the lower midsole 3 is not necessarily higher than the hardness of the upper midsole 2 and a hardness difference does not necessarily exist between the upper and lower midsoles 2, 3. That is because a rigidity of an area including the ridge lines 3 a ₁ of the lower midsole 3 is higher than rigidities of other areas even if the upper and lower midsoles 2, 3 have the same hardness.

Sixth Alternative Embodiment

In the above-mentioned embodiment and the first, third to fifth alternative embodiments, an example was shown in which the ridge lines 2 b ₁ of the wavy shapes of the upper midsole 2 or the ridge lines 3 a ₁ of the wavy shapes of the lower midsole 3 are vertically overlapped with the sole bent grooves G₁, G₂, G₃, G₃′ along the entire width of the sole (i.e. from the medial side end to the lateral side end of the forefoot region F) or the entire length of the sole bent grooves (see FIGS. 1 and 14), but application of the present invention is not limited to such an example.

A portion of each of the ridge lines 2 b ₁, 3 a ₁ may be vertically overlapped with the sole bent grooves G₁, G₂, G₃, G₃′. An overlapped area may be, for example, either one or two of a medial side part, a lateral side part, or a sole laterally central part of the forefoot region F. For example, the ridge lines 2 b ₁ may be vertically overlapped with the sole bent groove G₂ at the medial side part of the forefoot region F (that is, the ridge lines 2 b ₁ may be disposed opposite the sole bent groove G₂ in the vertical direction at the medial side part) and are not vertically overlapped with the sole bent groove G₂ at the lateral side part and the sole laterally central part of the forefoot region F (that is, the ridge lines 2 b ₁ are not disposed opposite the sole bent groove G₂ in the vertical direction at the lateral side part and the sole laterally central part). In this case, providing an additional explanation by referring to FIGS. 1 and 14, the ridge lines 2 b ₁ may be disposed inside the sole bent groove G₂ at the medial side part, but they are disposed outside the sole bent groove G₂ (not shown) at the lateral side part and the sole laterally central part. Any other suitable examples can be made in accordance with the requirements.

Seventh Alternative Embodiment

In the above-mentioned embodiment and the first and second alternative embodiments, an example was shown in which the sole bent grooves G₁, G₂ open both at the medial side end and at the lateral side end of the forefoot region F, but the sole bent grooves G₁, G₂ may open either at the medial side end or at the lateral side end of the forefoot region F, that is, the sole bent grooves G₁, G₂ close either at the lateral side end or at the medial side end of the forefoot region F. Alternatively, the sole bent grooves G₁, G₂ may close both at the medial side end and at the lateral side end of the forefoot region F. Similarly, the sole bent grooves G₃ may close at the medial side end and the sole bent grooves G₃′ may close at the lateral side end of the forefoot region F. Each of the sole bent grooves is not necessarily a continuous groove extending along the length of the groove and it may be a discontinuous groove along the length of the groove. Additionally, the ridge lines 2 b ₁ of the wavy shapes of the upper midsole 2 may have a length that corresponds to a length of each of the sole bent grooves. For example, in the event that a sole bent groove closes both at the medial side end and at the lateral side end of the forefoot region F, the ridge lines 2 b ₁ of the wavy shapes of the upper midsole 2 do not extend to the medial side end and the lateral side end of the forefoot region F. At the medial and lateral side ends, the wavy shapes of the upper midsole 2 may not appear.

OTHER APPLICATION

In the above-mentioned embodiments and each of the alternative embodiments, an example was shown in which the sole structure of the present invention was applied to the running shoe or indoor shoe, but the application of the present invention was not limited to such an example. The present invention also has application to other sports shoes.

As above-mentioned, the present invention is useful for a sole structure for a sports shoe that requires control of bendability of the forefoot region.

Those skilled in the art to which the invention pertains may make modifications and other embodiments employing the principles of this invention without departing from its spirit or essential characteristics particularly upon considering the foregoing teachings. The described embodiments and examples are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. Consequently, while the invention has been described with reference to particular embodiments and examples, modifications of structure, sequence, materials and the like would be apparent to those skilled in the art, yet fall within the scope of the invention. 

What is claimed is:
 1. A sole structure for a sports shoe disposed in a forefoot region of said sports shoe comprising: an upper midsole that is disposed on an upper side of said forefoot region of said sports shoe and that is formed of a soft elastic material; a lower midsole that is disposed on a lower side of said forefoot region, that has an upper surface adapted to contact a lower surface of said upper midsole, and that is formed of a soft elastic material; and an outsole that is disposed on a lower surface of said lower midsole, that has a ground contact surface adapted to contact a ground surface, and that has a sole bent groove extending substantially in a sole width direction, wherein both said lower surface of said upper midsole and said upper surface of said lower midsole have a corrugated surface that is formed of wavy shapes extending substantially in a sole longitudinal direction, ridge lines and trough lines of said wavy shapes extend substantially in the sole width direction, and said upper midsole and said lower midsole have a hardness difference, wherein at least a portion of said ridge lines of said wavy shapes of said upper midsole or said lower midsole that has a relatively higher hardness is overlapped with said sole bent groove of said outsole in a vertical direction.
 2. The sole structure according to claim 1, wherein said ridge line of said wavy shapes are overlapped with said sole bent groove in the vertical direction either at a medial side part, a lateral side part, or a sole laterally central part of said forefoot region.
 3. The sole structure according to claim 1, wherein said bent groove comprises a first sole bent groove and a second sole bent groove that are spaced apart on opposite sides of a metatarsophalangeal joint of a foot of a shoe wearer in the sole longitudinal direction.
 4. The sole structure according to claim 3, wherein a third sole bent groove is further disposed between said first sole bent groove and said second sole bent groove and said third sole bent groove is spaced apart from said first sole bent groove and said second sole bent groove in the sole longitudinal direction.
 5. The sole structure according to claim 1, wherein said sole bent groove opens at least at either one of a medial side end or a lateral side end of said forefoot region.
 6. The sole structure according to claim 1, wherein said sole bent groove closes at both a medial side end and a lateral side end of said forefoot region.
 7. The sole structure according to claim 1, wherein said sole bent groove includes a slit that extends through a thickness of said outsole.
 8. The sole structure according to claim 1, wherein said sole bent groove includes a recessed groove that is formed on said lower surface of said lower midsole.
 9. The sole structure according to claim 1, wherein said ridge lines and trough lines of said wavy shapes extend across an entire width of said forefoot region.
 10. The sole structure according to claim 1, wherein said ridge lines and trough lines of said wavy shapes are disposed only at a laterally central side portion of said forefoot region.
 11. A sole structure for a sports shoe disposed in a forefoot region of said sports shoe comprising: an upper midsole that is disposed on an upper side of said forefoot region of said sports shoe and that is formed of a soft elastic material; a lower midsole that is disposed on a lower side of said forefoot region, that has an upper surface adapted to contact a lower surface of said upper midsole, and that is formed of a soft elastic material; and an outsole that is disposed on a lower surface of said lower midsole, that has a ground contact surface adapted to contact a ground surface, and that has a sole bent groove extending substantially in a sole width direction, wherein either one of said lower surface of said upper midsole or said upper surface of said lower midsole has a corrugated surface that are formed of wavy shapes extending substantially in a sole longitudinal direction, ridge lines and trough lines of said wavy shapes extend substantially in the sole width direction, and at least a portion of said ridge lines of said wavy shapes is overlapped with said sole bent groove of said outsole in a vertical direction.
 12. The sole structure according to claim 11, wherein said ridge line of said wavy shapes are overlapped with said sole bent groove in the vertical direction either at a medial side part, a lateral side part, or a sole laterally central part of said forefoot region.
 13. The sole structure according to claim 11, wherein said bent groove comprises a first sole bent groove and a second sole bent groove that are spaced apart on opposite sides of a metatarsophalangeal joint of a foot of a shoe wearer in the sole longitudinal direction.
 14. The sole structure according to claim 13, wherein a third sole bent groove is further disposed between said first sole bent groove and said second sole bent groove and said third sole bent groove is spaced apart from said first sole bent groove and said second sole bent groove in the sole longitudinal direction.
 15. The sole structure according to claim 11, wherein said sole bent groove opens at least at either one of a medial side end or a lateral side end of said forefoot region.
 16. The sole structure according to claim 11, wherein said sole bent groove closes at both a medial side end and a lateral side end of said forefoot region.
 17. The sole structure according to claim 11, wherein said sole bent groove includes a slit that extends through a thickness of said outsole.
 18. The sole structure according to claim 11, wherein said sole bent groove includes a recessed groove that is formed on said lower surface of said lower midsole.
 19. The sole structure according to claim 11, wherein said ridge lines and trough lines of said wavy shapes extend across an entire width of said forefoot region.
 20. The sole structure according to claim 11, wherein said ridge lines and trough lines of said wavy shapes are disposed only at a laterally central side portion of said forefoot region.
 21. The sole structure according to claim 11, wherein said upper surface of said lower midsole or said lower surface of said upper midsole that does not have said corrugated surface has a planar surface, and wherein there is formed a gap between said planar surface and said lower surface of said upper midsole or said upper surface of said lower midsole. 